Unit testing update (#199)

CryptoExchange.Net/Interfaces/IAuthTimeProvider.cs

@@ -0,0 +1,16 @@
+using System;
+
+namespace CryptoExchange.Net.Interfaces
+{
+    /// <summary>
+    /// Time provider
+    /// </summary>
+    internal interface IAuthTimeProvider
+    {
+        /// <summary>
+        /// Get current time
+        /// </summary>
+        /// <returns></returns>
+        DateTime GetTime();
+    }
+}